Manner and device null in order to do the be adapted thresholding of the gray scale

摘要

A method and apparatus for adaptively adjusting (e.g. thresholding) grayscale image data associates with each document image file (210, 212) a predetermined grayscale adjusting function (216) which can be used to threshold, contrast stretch and gray level reduce the original gray level image of the document into a picture representation for display at workstations, the picture representation yielding increased contrast of written and printed text viewed. The invention includes a method of generating a remapping function for use in converting near-photographic document image pixel gray level data lying in a first range of gray level values to higher contrast, background-suppressed pixel gray level data lying in a second more limited gray level range. Global document information, such as a histogram of all the document's original pixels, is used to generate at least one threshold gray level value and to determine the shape of the remapping function on either side of the threshold. Preferably, the remapping function is implemented by a look-up table (216) addressed in accordance with the original pixel data.